The present invention relates to x-ray systems and more particularly to apparatus for providing to a user a medically useful stereoscopic densitometric image of a three dimensional object such as a human breast.
While it has previously been proposed to implement stereoscopic visualization of x-ray images, such prior art systems have apparently not been medically successful for various reasons, largely failure to produce left and right images which can be successfully fused without visual strain by normal viewers such as medical doctors. As is understood by those skilled in the field of visual perception, the successful fusing of left and right images to obtain a natural and meaningful stereoscopic visualization is easily disrupted by any of a large number of possible imperfections or inconsistencies in the two images which are to be fused. For example, if the left and right images are generated on different cathode ray tubes (CRTs), as in the Sklebitz et al. disclosure of U.S. Pat. No. 4,769,701 it is extremely difficult to obtain to avoid differences in scale and in registration between the two tubes. Mis-registration, particularly in the vertical direction, is extremely disturbing to the ability of most viewers to effect subjective fusing of the images. Like Sklebitz et al., the system shown in the Simon Pat. No. 3,073,05 utilizes a pair of CRTs for display. Similarly, if different cameras or different regions of the same vidicon camera are utilized for the left and right images, e.g., as proposed in the Itoh U.S. Pat. No. 4,578,802, registration of the images may depend upon essentially perfect linearity of the vidicon scanning. Further, the spatial resolution of the vidicon tube is typically not adequate. In the Itoh system the right viewed and left viewed visual images are simultaneously displayed on a monitor with separation being effected by polarized glasses or a lenticular sheet system. Neither of these are described in detail but are believed to involve differentiating masks over the face of the monitor.
It has also been proposed to differentiate left and right images by utilizing different colors, e.g., as in the Euler et al. disclosure of U.S. Pat. No. 3,309,519. However, while the fusing of left and right images of different color can be accomplished, though with some difficulty, when viewing essentially solid objects, it becomes difficult in the extreme when the three dimensional images are densitometric, as in the case of x-ray images, so that the user's view in effect penetrates the object being viewed. This problem is particularly acute where the features being looked for, such as tumors and calcifications in the case of a human female breast, may exhibit only subtle densitometric differentiation from surrounding tissue.
There is also substantial prior art regarding the taking of stereotaxic images of an object such as a human breast but the purpose of obtaining such images is to facilitate the accurate placement of a localization needle within the object which is accomplished by the localization of visual landmarks in each of two images from points of view separated by a relatively wide angle and the images are not intended to be viewed simultaneously or fused by the user to yield a true three-dimensional view.
Among the several objects of the present invention may be noted the provision of a novel stereoscopic x-ray system which allows a user to readily fuse left and right viewed images so as to achieve stereopsis; the provision of such a system which provides highly accurate registration and matching of left and right viewed images; the provision of such apparatus which allows the stereoscopic visualization of features which are subtly differentiated in density; the provision of such a system which allows great flexibility in the presentation of stereoscopic x-ray images; the provision of such a system which provides highly accurate and medically useful visualization; and the provision of such a system which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.